1. Field of the Invention
The present invention relates to an image reading apparatus.
2. Description of the Related Art
As a unit for reading image information on each side of documents piled on a document tray during conveying process, a so-called ADF (Auto Document Feeder) has been known for a long time.
The ADF is classified by the presence of a document reversing unit and a reading out unit as follows.
(1) Single-sided document ADF (FIG. 5):
Documents piled on a document tray 1001 are separated one by one, and conveyed onto a platen 1002, so as to read out images in an image reading unit 1003, and then, are discharged.
(2) Double-sided document ADF with a turning-over unit (FIG. 6):
After the first side is read out by the image reading section 1003, the document is turned over by a turning-over unit 1005 so as to convey the turned-over document on the platen 1002 again so as to read out the rear side as the second side.
(3) Double-sided document ADF with reading units (FIG. 7):
In an ADF device, a first reading unit 1006 and a second reading unit 1007 are arranged along a document transfer path so as to simultaneously read both sides during conveying the document.
Among above three ADFs, although (1) is most inexpensive, it cannot read out double-sided documents automatically so as to have a fault of low productivity.
In the double-sided document ADF with the turning over unit of (2), since after separating one document from the documents on the document tray so as to convey it to a predetermined reading position for reading out one side, it is turned over and conveyed to the predetermined reading position again for reading out the other side and being discharged thereafter. Because of this double-sided reading procedure, there is a problem of low reading efficiency.
Also, since the transfer path becomes complicated, a problem may arise in that a document may be damaged during transferring.
Then, as for the double-sided document ADF with the reading units (3), since both sides are simultaneously read during the conveying of the document using two optical systems, although it is expensive, this is very excellent in productivity in comparison with other ADFs.
When the three ADFs are compared, the double-sided document ADF with the reading units of (3) is most excellent in productivity, so that this type of ADF may make progress quickly from now on.
In common double-sided document reading ADFs, as disclosed in Japanese Patent Publication No. 2928449, a first reading unit for reading one side and a second reading unit for reading the other side are arranged above and below with a document conveying path therebetween so that a document is read out through openings of guide plates.
However, this type of ADF with the reading units employs a so-called reduction optical system for the other side reading unit, which includes a light source, a plurality of turnover mirrors, a lens, and a CCD, so that the reading unit itself is large in size.
Therefore, the transfer path is substantially straight from paper feeding to discharge, so that the discharge tray is forced to protrude outside the ADF.
Then, Japanese Patent Laid-Open No. 11-69086 and Japanese Patent Laid-Open No. 11-327221 propose techniques for solving such problems.
The double-sided document reading apparatus described in the publication reduces the entire apparatus in size using a contact-type sensor instead of a reduction optical system so as to form a U-turn path.
In order to treat paper jamming not only for the ADF but for a paper conveying device, it is desirable to have an open/close mechanism for a transfer path.
Since the U-turn path becomes complicated more than a straight path, the open/close mechanism is especially indispensable.
Also, when dust exists in a document reading portion of the other-side reading unit, image defects such as black streaks and white streaks may be produced. Therefore, the maintenance for the document reading portion of the other-side reading unit must be easily performed, so that a mechanism for opening the document reading portion is indispensable.
In the double-sided reading apparatus disclosed in Japanese Patent Laid-Open No. 11-69086 or No. 11-327221, the contact-type sensor for reading the other side is arranged inside a transfer guide of the U-turn path.
Also, the double-sided reading apparatus disclosed in Japanese Patent Laid-Open No. 11-327221 has a two-stepped open/close hinge located at the end of the apparatus so as to achieve to treat the jamming inside the U-turn path; however its structure is very complicated and the mechanism itself is expensive.
Although the Japanese Patent Laid-Open No. 11-69086 does not specify an open/close mechanism of the transfer path in the vicinity of the contact-type sensor, the contact-type sensor is arranged in the lower portion of the feeding tray so as to have a considerably complicated arrangement. Therefore, when the open/close mechanism is to be adopted, the considerably complicated mechanism cannot be avoided.